JPS6144277B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating a radioactive liquid containing ammonium nitrate, ammonium carbonate, and uranium or plutonium as carbonate in solution, produced, for example, in the AUC method or the AUPuC method.

West German Patent Application Publication No. 1952477 and
In the AUC method detailed in No. 1592471,
If uranyl nitrate was the starting product, a solution would result with the following composition:

Approximately 100g of _NH4 per unit Approximately 150g of NO3 per unit Approximately 90g of _CO3 per unit Approximately 300g of U per unit Approximately 100g of _NH4 per unit Approximately 300g of U per unit of NH4 Approximately 300g of U per unit Approx. A plutonium component is produced.

If unirradiated plutonium-free uranyl nitrate is used as the starting product, the liquid resulting from nuclear fuel production must be sufficiently chemically purified of uranium and its decomposition products to avoid contaminating the environment with radioactivity. After separation, it can be discharged into the sewer.

However, such release is not allowed if irradiated uranium or plutonium is contained. In such cases, decontamination by chemical methods is insufficient.

Since the volume of the liquid produced in the nuclear fuel manufacturing process is relatively large, it cannot be released for final storage even after some solidification treatment, so it is necessary to reduce the volume as much as possible.

In this case, complete evaporation is not allowed due to the explosion hazard posed by the ammonium nitrate. However, since water needs to be separated from radioactive components due to volume reduction, the ammonium nitrate must be decomposed.

There are several methods for pyrolyzing such nitrates at temperatures above 250°C, in which case water is evaporated along with the decomposition products. In that case, radioactive components remain in the reaction vessel.

This method has the disadvantage that the liquid is only decomposed if it has been evaporated to about 75-80% NH ₄ NO ₃ beforehand, and the risk of explosion cannot be ruled out. Moreover, the resulting decomposition products cannot be recovered or can only be reused at great expense. It should be noted that the relatively high temperature level does not immediately make the above thermal treatment method cheaper, and furthermore, the relatively high temperature level does not immediately make the above thermal treatment method cheaper, and furthermore,
It must be mentioned that purification from the body is equally problematic.

Therefore, the challenge is to develop an economical method that not only allows the radioactive components to be easily separated, but also allows the resulting decomposition products to be recovered into the fuel manufacturing process. Furthermore, it must be possible to eliminate the risk of explosion.

To electrolytically treat a radioactive filtrate containing ammonium nitrate, ammonium carbonate, and uranium or plutonium as a carbonate complex,
The preheated filtrate is introduced into the cathode chamber of the electrolytic cell containing a boiling ammonium nitrate solution, where the filtrate is raised to boiling temperature under the combined action of the boiling ammonium nitrate and the Joule heat of the electrolytic current, and its contents are ammonium carbonate and free ammonium are released as gaseous CO ₂ and NH ₃ , these gases are discharged together with the water vapor and NH ₃ electrolytically formed from NO ₃ generated at the time, and as the carbonate complexes mentioned above. The uranium or plutonium initially present in the solution is precipitated as deuterate or plutonium hydroxide and separated by constant circulation of the tank contents through a filter and by electrolysis at the cathode, and This is achieved by electrolytic cathodic deposition. The voltage of the electrolytic cell is then adjusted in such a way that the heat output of the electrolytic current produced thereby results in the evaporation of a volume of liquid approximately equal to the volume of liquid introduced. Therefore, this method is a continuous treatment method in which the volume of introduced liquid corresponds to the volume evaporated by electrolysis.

Embodiments of the present invention will be described in detail below with reference to the drawings.

The drawing shows an apparatus for carrying out the method described above. The electrolytic cell 1 consists of a cylindrical container, which is provided with an annular anode 2 made of, for example, sand-grained graphite, layered titanium, or iron, and a rod-shaped cathode 3 made of special steel. The cylindrical intermediate wall 11 is made of special steel from the lid wall of the electrolytic cell 1 to several centimeters below the electrolyte level 8, followed by a chemically resistant porous material such as polypropylene fabric. The cathode chamber 31 is made of an insulating material and extends downwardly beyond the lower end of the electrode.
1 from the anode chamber 21, thus making it possible to take out the reaction products reliably.

A heat exchanger 6 is present in the anode chamber of the electrolytic cell, and its inlet side is connected to a supply conduit 7 for the liquid to be treated, and its outlet side is connected via a conduit 76 to the supply connection tube 32 of the cathode chamber 31. ing. A conduit 53 leading to the filter 5 is also connected to the connecting pipe, and the filter 5 is connected to the discharge connecting pipe 24 via the pump 4. Like the cathode chamber 31, the anode chamber 21 is filled with electrolyte up to the liquid level 8 slightly above the anode 2.
A gas exhaust conduit 22 is provided in the cathode chamber 31, and a gas exhaust conduit 33 is provided in the cathode chamber 31. A discharge valve 12 is provided at the bottom of the electrolytic cell 1 .

The method carried out by the above device proceeds as follows.

A boiling ammonium nitrate solution having a concentration of approximately 250 g/l is first introduced into the cathode and anode compartments as an electrolyte. The liquid to be treated is then supplied via conduit 7. Before entering the electrolytic cell 1, the liquid first passes through a heat exchanger 6, where it is preheated and reaches the boiling electrolyte via a conduit 76 and a connecting tube 32. Said preheating is carried out by the discharge conduit 3
Gas discharged from 3 (not shown)
It can also be enhanced by heat exchange bonding.

In order to avoid the generation of harmful cathodic hydrogen at the cathode 3, some copper is initially added to the solution, so that the cathode 3 essentially acts as a copper electrode. The properties of copper are maintained in the cathode 3 at all times because new precipitation always occurs due to partial melting of the copper coating.

The liquid supplied via the connecting pipe 32 likewise begins to boil, releasing its ammonium carbonate and free NH ₃ content in the gaseous form CO ₂ and NH ₃ . Preferably, these gases are discharged together with the water vapor produced by boiling through conduit 33 and fed back into the fuel production process. Therefore, the liquid becomes an ammonium nitrate solution containing a small amount of uranium or plutonium. At around 100℃
Due to the low solubility of NH ₃ , automatically a PH of about 6-7
A value is created. The concentration of CO ₃ that may be present in this case is extremely low. Thus, the uranium or plutonium that was previously present in solution as a carbonate complex is precipitated as a deuterate or plutonium hydroxide.

The electrolyte is circulated throughout by means of a pump 4, the precipitate which continuously forms being removed in this case by means of a strainer 5 located in the pump line. In that case, the feeding direction of the pump is from the anode chamber 21 to the cathode chamber 31 as shown. Because CO ₂ is not 100% removed, a small amount of uranium (plutonium) remains dissolved. However, these dissolved uranium are precipitated cathodically by electrolysis and can therefore be dissolved from the cathode 3 by the acid during shutdown.

Apart from a slight precipitation of uranium, NO ₃ ^- is reduced to NH ₃ by the electrolytic process and dissipated in the heat of boiling. Water is converted to _O2 anodically. By consciously utilizing the heat generated during electrolysis, which is generally undesirable, the electrolyte is kept at a boiling state.
Ammonium carbonate can be decomposed, ammonia eliminated and water in solution evaporated.

Such joule heat is regulated by the voltage of the electrolyzer, which is typically a few volts, such that the volume of liquid evaporated is equal to the amount of decomposed ammonium carbonate contained within that volume. Similarly, this value corresponds to the amount of liquid supplied. The process according to the invention is therefore carried out completely continuously at a constant concentration and conversion rate.

The electrolytic cell 1 is constructed as shown because, as already mentioned, oxygen is evolved at the anode and this oxygen can form an explosive mixture with NH ₃ . This structure operates so that the current density in the anode chamber 21 is lower than the current density in the cathode chamber 31, since only the cathode chamber is kept in a boiling state. Fresh liquid is supplied only to the cathode compartment, where the reduction of NO ₃ to NH ₃ takes place, so that NH ₃ is dissipated only from the cathode compartment.
Since the cathode chamber is separated from the anode chamber by a separation wall 11, oxygen generated at the anode and
Mixing with NH ₃ is reliably prevented. The oxygen is discharged via conduit 22 and diluted with air added via conduit 23.

The safety aspect already mentioned several times, in which the risk of explosion is avoided in the method and the device described above, can also be achieved by immersing the electrodes 2 and 3 to approximately half the depth of the electrolyte. can be expected. According to this, even if the supply of liquid via the conduit 7 happens to fail, and also in the event of a failure of the adjustment mechanism (not shown in the drawings), the concentration of the solution present in the tank will remain constant. It is guaranteed that it can only double due to its evaporation. This is because in that case both electrodes are no longer immersed in the solution and the evaporation therefore ends automatically. This concentration is not dangerous at all.

In summary, conventional pyrolysis processes proceed at a temperature of 250°C, whereas the temperature level in the method of the present invention remains at about 100°C. Heat conduction is direct and therefore virtually lossless. The radioactive components are most simply and dust-free separated in the reactor and removed therefrom in a known manner.
The reaction products generated at this time can be discharged harmlessly into the atmosphere, but they can also be recycled, that is, returned to the fuel production process (AUC method). The deposited product removed from the filter is already highly concentrated compared to its starting volume and, after further solidification in a known manner, can be treated as radioactive waste or reused. You can let me. The electrolytically separated uranium or plutonium is fed back to the fuel production process in a known manner.

[Brief explanation of the drawing]

The drawings are schematic configuration diagrams of a liquid processing electrolytic cell and a liquid circulation device of the present invention. DESCRIPTION OF SYMBOLS 1... Electrolytic cell, 2... Annular anode, 3... Rod-shaped cathode, 4... Pump, 5... Passer, 6...
...Heat exchanger, 7...Filtrate supply conduit, 8...Liquid level of electrolyte solution, 11...Intermediate wall, 12...Discharge valve, 21
...Anode chamber, 22...Gas exhaust pipe, 23...
...Air conduit, 24...Discharge connection pipe, 31...Cathode chamber, 33...Gas exhaust pipe.

Claims (1)

[Claims] 1. In order to electrolytically treat a radioactive filtrate containing ammonium nitrate, ammonium carbonate, and uranium or plutonium as a carbonate complex in solution, a cathode of an electrolytic cell in which a preheated filtrate is charged with a boiling ammonium nitrate solution. The filtrate is brought to boiling temperature under the joint action of this boiling ammonium nitrate and the Joule heat of the electrolytic current, and the ammonium carbonate and free ammonium it contains are converted into gaseous CO ₂ and NH ₃ . These gases are emitted along with the water vapor and NH ₃ electrolytically formed from NO ₃ produced at the time, and the uranium or plutonium originally present in solution as the carbonate complex is converted into a diuranate. A method for the treatment of radioactive filtrate, characterized in that it is precipitated as plutonium or plutonium hydroxide and separated by constant circulation of the tank contents through a filter and by electrolysis at the cathode. 2. A method according to claim 1, characterized in that the voltage of the electrolytic cell is adjusted such that the heat output of the electrolytic current causes the evaporation of a volume of liquid approximately equal to the volume of the supplied filtrate. 3. Process according to claim 1 or 2, characterized in that some copper is added to the filtrate containing ammonium nitrate.